Well, Moln, there is absolutely no way they would forgive an Irish "terrorist" and welcome him into the family. Much less got the Government to let him stay in Downton.
Also, what year is it? Because the war of independence was pretty much over by 1921, and the Irish were fighting each other not the British by then.
And it's all a bit simplistic. It just doesn't ring true.
But then, the way they talk to their servants and allow opinions doesn't really ring true either, so calling a chauffeur Tom isn't much stranger than that.
I'm just a bit disillusioned. There are more interesting social changes going on in Britain rather than just wheeling out the "Irish question" half-heartedly.